Add state guard to WebRTC connection controller

WebRtcSessionDescriptionFactory forcibly flushes its callbacks during
destruction. When the WebRtcSessionDescriptionFactory executes a pending
callback, it runs after the parent PeerConnection has begun destruction.
This results in an immediate crash if the callback attempts to access or
modify members of the already dying PeerConnection object.

Example backtrace:
0  webrtc::WebRtcSessionDescriptionFactory::SdesPolicy() const ()
1  webrtc::SdpOfferAnswerHandler::ValidateSessionDescription()
2  webrtc::SdpOfferAnswerHandler::DoSetLocalDescription()
3  rtc::rtc_operations_chain_internal::OperationWithFunctor::Run() ()
4  webrtc::SdpOfferAnswerHandler::SetLocalDescription()
5  webrtc::PeerConnectionProxyWithInternal()
6  webrtc_streaming::ConnectionController::OnCreateSDPSuccess()
7  CreateSessionDescriptionObserverIntermediate::OnSuccess()
8  WebRtcSessionDescriptionFactory::~WebRtcSessionDescriptionFactory()
9  webrtc::PeerConnection::~PeerConnection() ()
10 rtc::RefCountedObject<webrtc::PeerConnection>::~RefCountedObject() ()

This change adds an explicit IsShuttingDown() state guard in the
connection controller. This ensures that any callback triggered during
destruction safely exits before attempting to access objects being
destroyed.

Author: MikkoAtWork

base/cvd/cuttlefish/host/frontend/webrtc/libcommon/connection_controller.cpp

@@ -89,7 +89,8 @@ ConnectionController::ConnectionController(
     ConnectionController::Observer& observer)
     : sig_handler_(sig_handler),
       connection_builder_(connection_builder),
-      observer_(observer) {}
+      observer_(observer),
+      shutting_down_(false) {}
 
 void ConnectionController::CreateOffer() {
   // No memory leak here because this is a ref counted object and the
@@ -114,6 +115,11 @@ Result<void> ConnectionController::RequestOffer(
 }
 
 void ConnectionController::FailConnection(const std::string& message) {
+  if (shutting_down_) {
+    // Don't bother signaling the error during connection teardown
+    LOG(ERROR) << message;
+    return;
+  }
   Json::Value reply;
   reply["type"] = "error";
   reply["error"] = message;
@@ -189,6 +195,7 @@ Result<void> ConnectionController::OnErrorMsg(const std::string& msg) {
 
 Result<void> ConnectionController::OnCreateSDPSuccess(
     webrtc::SessionDescriptionInterface* desc) {
+  CF_EXPECT(!shutting_down_, "Operation aborted during connection teardown.");
   std::string offer_str;
   desc->ToString(&offer_str);
   std::string sdp_type = desc->type();
@@ -225,6 +232,11 @@ void ConnectionController::OnSetLocalDescriptionFailure(
 
 void ConnectionController::OnSetRemoteDescriptionComplete(
     const webrtc::RTCError& error) {
+  if (shutting_down_) {
+    LOG(WARNING) << "OnSetRemoteDescriptionComplete aborted on "
+                 << "connection teardown";
+    return;
+  }
   if (!error.ok()) {
     // The remote description was rejected, can't connect to device.
     FailConnection(

base/cvd/cuttlefish/host/frontend/webrtc/libcommon/connection_controller.h

@@ -131,6 +131,8 @@ class ConnectionController : public webrtc::PeerConnectionObserver {
   void OnRemoveTrack(
       rtc::scoped_refptr<webrtc::RtpReceiverInterface> receiver) override;
 
+  void Shutdown() { shutting_down_ = true; }
+
  private:
   friend class CreateSessionDescriptionObserverIntermediate;
   friend class SetSessionDescriptionObserverIntermediate;
@@ -166,6 +168,7 @@ class ConnectionController : public webrtc::PeerConnectionObserver {
   PeerConnectionBuilder& connection_builder_;
   Observer& observer_;
 
+  bool shutting_down_;
   rtc::scoped_refptr<webrtc::PeerConnectionInterface> peer_connection_;
   std::vector<std::unique_ptr<webrtc::IceCandidateInterface>>
       pending_ice_candidates_;

base/cvd/cuttlefish/host/frontend/webrtc/libdevice/client_handler.cpp

@@ -85,6 +85,10 @@ ClientHandler::ClientHandler(
       data_channels_handler_(observer),
       camera_track_(new ClientVideoTrackImpl()) {}
 
+ClientHandler::~ClientHandler() {
+  controller_.Shutdown();
+}
+
 rtc::scoped_refptr<webrtc::RtpSenderInterface>
 ClientHandler::AddTrackToConnection(
     rtc::scoped_refptr<webrtc::MediaStreamTrackInterface> track,

base/cvd/cuttlefish/host/frontend/webrtc/libdevice/client_handler.h

@@ -60,7 +60,7 @@ class ClientHandler : public ConnectionController::Observer,
       PeerConnectionBuilder& connection_builder,
       std::function<void(const Json::Value&)> send_to_client_cb,
       std::function<void(bool)> on_connection_changed_cb);
-  ~ClientHandler() override = default;
+  ~ClientHandler() override;
 
   bool AddDisplay(rtc::scoped_refptr<webrtc::VideoTrackInterface> track,
                   const std::string& label);